1. Field of the Invention
This invention relates to a composite structural body comprising a honeycomb or corrugated core, a plain sheet and a pressure sensitive adhesive layer, and more particularly to a novel and practical sound damping material which is characterized by directly applying a pressure sensitive adhesive layer to one or both surfaces of a honeycomb or corrugated core and has an excellent damping performance over a wide frequency range and is very small in the temperature dependence and suitable for weight-saving and cost reduction.
2. Description of the Prior Art
With the spread of vehicles such as automobiles, trains, airplanes and the like as well as office machines, electric appliances and so on, a countermeasure for reduction of noise generated by these devices is needed. As a result, it is well-known that many sound damping materials are patented and on the market now.
In order to use these sound damping materials against the instrument or equipment which is the noise source, it is practically required to have the following conditions:
(1) the damping effect is large at low and middle frequency ranges; PA1 (2) the damping effect does not reduce over a wide temperature range; and PA1 (3) the weight is as light as possible and the cost is low.
As to condition (1), an oscillation frequency in many apparatus, instruments and equipments requiring noise control is not more than 1,000 Hz (Noise Control Handbook, Associate of Japanese Acoustic Material, pp. 97-171), and particularly it is within a range of dozens to several hundreds Hz in the automobiles and the like. Concerning condition (2), these apparatus and the like are frequently used over a wide temperature range, for example, from a low temperature near 0.degree. C., to 60.degree.-80.degree. C., sometimes a high temperature of around 100.degree. C., so that it is naturally desired to develop a satisfactory damping effect at such a temperature range. As to condition (3), it is important to lighten the total weight of the apparatus such as automobile or the like as far as possible in view of energy-saving and cost reduction.
In conventional sound damping materials, particularly sound damping sheets, the damping effect per unit weight is low and the temperature dependence of the damping performance is large, especially the damping effect at a high temperature range largely reduces (see Comparative Example 4 as mentioned later). Therefore, they are considerably restricted in their application range against the above mentioned conditions at present.